Automatic pilot for mobile craft



June 23, 1953 A. M. MaOCALLUM EIAL 2,543,354

AUTOMATIOPILOT FOR MOBILE CRAFT Filed May l9, 1948 I6 I I J INVENTORS' CHARLES RUSSELL ALAN M. M

CALLUM v 24,

Patented June 23, 1953 AUTOMATIC PILOT FOR MOBILE CRAFT Alan M. MacCallum, Plainfield, and Charles Russell, Englewood Clifis, N. J assignors to Bendix Aviation Corporation, Teterboro, N. J a corporation of Delaware Application May 19, 1948, Serial No. 28,028

9 Claims.

This invention relates to automatic pilot systems for mobile craft, and more particularly to a steering surface control for mobile craft operative in response to a direction device.

An object of our present invention is to provide a rudder control for a mobile craft responsive to direction signals in which a repeater station for the direction signals is provided and where the direction signals may be varied to provide a course selector for the craft.

A further object of our invention is to provide a rudder displacement signal in an automatic pilot system of the character indicated, which provides the necessary reverse rudder action as the craft is brought about onto the preset course to prevent overshooting of the course.

Another object of this invention is to provide a rudder control system of the character indicated in which the natural period and response of the craft to rudder actuation is compensated for by the inclusion of a time delay or rate circuit in the system to maintain the craft on its preset course.

Still another object of the present invention is to provide a rudder control system of the general character described in which a continuously operated motor is used for actuating the rudder, the direction of rudder displacement being controlled electromagnetically by the operation of the system to provide correct rudder displacement for maintaining the craft on its course.

Still a further object of our invention is to provide a rudder control system of the character described which shall consist of few parts, relatively inexpensive to manufacture, which shall be positive and automatic in its operation, have a large variety of applications, and yet be practical and efiicient to a high degree in use.

Other objects of the invention Will in part be obvious, and in part hereinafter pointed out.

Referring now to the single figure of the drawings in which one of the various possible illustrative embodiments of our invention is shown as a schematic wiring diagram, the numeral I designates a circuit interconnecting a source of compass signal voltage II with a rudder actuating means generally designated by the numeral l2. 7 The source of compass signal voltage comprises an earth inductor type of element arranged and mounted below and parallel to, a magnetic compass so that the deflection of the compass needle will induce in the three-phase stator winding l5, a component of the earths magnetic field. The rotor winding I4 is connected across a suitable source of alternating current [6 and 2 saturates the stator winding core (not shown). A voltage will be induced in the stator winding 15 which is dependent upon the magnetic deflection of the compass needle.

The induced voltages in the stator winding 15 are impressed on a course setter 20 herein shown as a potentiometer winding 2| having two diametrically opposed wiper contacts 22 adapted to be rotated by a knob 23. The potentiometer winding 2| is divided at three points degrees apart, each of the three legs of the winding being connected across a phase of the stator I5 by the leads 25. The signal voltage appearing across each of the respective legs of the potentiometer winding 2| is of the second harmonic, as is Well known in the art. The wiper contacts 22 of the course setter will pick up the vector sum of the voltages appearing in the legs of the potentiometer winding 2|. This signal voltage appearing across the wiper contacts 22 is applied by the lead 26 and by a lead 21 through the series connected resistors 28 and 29 to the primary winding 30 of a transformer 3!. The secondary winding 32 of the transformer is center-tapped to ground as at 33. The ends of the secondary winding are connected to the control grids 34 and 35 of the two tetrode sections making up the tube 36.

The tube 36 comprises two indirectly heated cathodes 31 and 38, two screen grids 39 and 40, the two control grids and two plates 4] and 42. The two sections of the tube 36 are connected in parallel and form a phase discriminator circuit. The plate 4| of the upper section is connected by a lead 45 through a relay coil 46 to a power lead 41 of a suitable source of alternating current. The plate 42 is also connected to the power supply 41 through a relay coil 48 by a lead 49. The frequency of the power supply 41 is double that of the power supply Is. The screen grids 39 and 40 are interconnected by a lead 5| to the power lead 47, while the cathodes 31 and 38 are suitably connected to a source of bias voltage (not shown).

The relay coil 46 has associated therewith a switch arm 53 adapted to engage a fixed contact 54 upon energization of the relay coil 46. The relay coil 48 is similarly provided with a switch arm 55 and a fixed contact 56. The switch arms 53 and 55 are electricallyinterconnected and connected by a lead 51 to one terminal of a source of potential 58. The fixed contact 54 of the relay 46 is connected by a lead 59 to one end of a solenoid coil 60, the other end of said coil being connected by a lead 6| to the other terminal of the power supply 58. The fixed contact 56 of the relay 48 is connected by a lead 62 to one end of a c ond solenoid coil 63, the other end of said coil being connected to the power lead 6i.

The phase discriminating circuit described will the rudder actuating mechanism l2 to l the rudder in the proper direction in response to the signal voltages. It will be understood by those versed in the art, that at any 9 cut-of-phase 180 degrees. As the voltage on the plate ii rises to a positive value, the voltage on plate d2 will fall to a negative value. The phase of the signal voltage impressed across the centertapped secondary winding 32 of the transformer 3! will be dependent upon the angular position of the compass needle with respect to the threephase winding 15. This signal voltage will also be an alternating potential so that while the signal on the grid 34 is increasing to a positive value, the potential on the grid 35 will be decreasin to a negative value. Dependent, therefore, on the phase of the plate voltage and the grid voltage at any given instant will determine which section of the tube 38 will operate. The conduction of the section of the tube including the plate ll will energize the relay 48, while the conduction of the other section of the tube will energize the relay 7.8.

Energization of the relay 45 will attract the switch arm 53 to close the switch arm and the fixed Contact An energizing circuit will thus be completed for the solenoid 60. This circuit be traced from the power lead 6! through th solenoid coil through the lead 59, the fixed contact and switch arm 53 and thence through the power lead 5? through the other terminal of the source of power 58. The energization of the relay 58 by the lower section of the tube will close the switch arm 55 and the fixed contact 56 to complete a similar circuit for the solenoid 63.

The solenoids it and 83 form a part of the rudder actuating mechanism 12. The rudder actuating mechanism comprises in addition, a con tinuously operating motor 65 operating through a differential mechanism 65 to actuate the rudder (not shown) through suitable gearing herein shown by the dashed line 81. The differential device is provided with a braking mechanism 69 and 78 adapted to be actuated respectively by the solenoid 63 and 66.

For a more complete description of the differential mechanism 63 reference may be had to the copending application of Alan M. MacCallum for Differential Servo with Continuously Runnin l'vl'otor filed on May 25, 1948, and bearing Serial No. 29,085, now abandoned. For a more detailed description of the braking mechanism 69 and 79, reference may be had to the copending application of Charles E. Gregory for a Balanced Brake Linkage bearing Serial No. 29,333 and filed on May 26, 1948.

The operation of the rudder actuating mechanism E is such that with the motor 65 operating and neither solenoid 65 or 53 energized, no output will be obtained from the differential mechanism 56. The rudder will, therefore, remain stationary in its neutral position. The development of a signal voltage across the leads 2'! and 25 will operate either the solenoid 65 or 83 depending upon its phase. By the operation of either of the solenoids, the brake mechanism associated with the differential mechanism will be set by the energized solenoid to hold one half of the differential mechanism permitting the output thereof to be rotated in a given direction. The output of the diilerential 66 as applied to the rudder by the gearing B? will deflect the rudder in a direction responsive to the phase of the signal voltage.

Means is now provided to offset the signal voltage appearing across the leads 2'! and 28 by a displacement signal voltage responsive to rudder position.

To this end there is provided a bridge potentiometer 75 having a continuous resistor 76 provided with two diametrically opposed wiper arms H. The wiper arms 77 are adapted to be rotated through suitable gearing 78 upon operation of the difierential mechanism in response to the signal voltages. Two diametrically opposite points 79 on the resistor wire '15 are connected by the leads 88 across the alternating power supply 4'1. The two wiper arms H are connected by the leads 8i across the resistor 28 in the output lead. 21 of the course setter. The connection is so made that the signal of the bridge potentiometer is in opposition to the signal of the course setter. It will be noted in passing that when the rudder of the ship is in its neutral position, the wiper arms 37 will be in a position on the resistor winding which will equally divide the winding into four equal arms at which point no output voltage will be provided by the potentiometer across the resistor 23.

In the operation of the mecham'sm thus far described, the signal voltage provided by the course setter will operate the rudder in the manner described. The operation of the differential mechanism 66 in positioning the rudder will at the same time move the wiper arms I? to provide an unbalanced condition of the bridge 75. This unbalanced condition of the bridge will provide a displacement signal which will oppose the signal voltage due to the compass signal. The two signals will tend to offset each other in anticipation of the craft coming about on the preset course. The ener ized solenoid will then become de-energized. The rudder displacement signal left in the circuit will reverse the operation of the differential mechanism 66 to provide a reverse rudder action to bring the rudder back to its neutral position.

The compass signals developed in the stator windings l5 are repeated in the three legs of the potentiometer 2| of the course setter. By rotating the knob 23 of the course setter, the wiper contacts 22 will be rotated over the potentiometer wire to provide a signal voltage which is dependent on the compass signal and the position of the wiper contacts. Thus, for a given course setting, the signal voltage appearing across the leads 26 and 21 will depend upon the heading of the craft. When the heading of the craft corresponds to the course set in, no signal voltage will appear across the leads 26 and 21 under normal conditions. The position of the compass needle with respect to the stator I5 and the position of the wiper contacts 22 with respect to the three legs of the potentiometer are such that no signal voltage will appear across the leads 26 and 21. With no signal voltage across the leads, both solenoids 60 and 63 will remain de-energized, the rudder being in its neutral position.

Upon craft deviation from the course set into the course setter 20, a condition of unbalance will exist which results in a signal voltage across the leads 26 and 27. Depending upon the direction of course deviation, the signal voltage will operate either the solenoid 60 or 63 in response to the phase of the signal voltage. The rudder will then be actuated to return the craft to the preset course in the manner already described.

Due to the inertia of the ship and its slow response to rudder movement, the circuit thus far described will tend to overshoot the preset course on changes in course or large deviations from the preset course. A damping circuit based upon the natural period of the ship and its response to rudder actuation is provided and herein illustrated as a rate circuit generally designated by the numeral I00. The rate circuit comprises an input transformer IOI having a primary winding I02 connected by the leads I03 across the output leads 26 and 21 of the course setter 20. The secondary winding I03 of the transformer is center-tapped to ground and provides the input for a phase discriminator circuit I04 similar to that of the tube 36. The phase discriminator I04 comprises two triode sections I05 and I06, the output of which is connected to a time delay device H0. The time delay device IIO forms a part of a bridge circuit II2, the unbalance of which will provide a rate signal across the leads II3 which is then applied across the resistor 29 of the lead 21 in opposition to signal voltage. The time delay device comprises two resistors H5 and H6 in heat exchange relationship with two resistors I I1 and I I8, sealed in an envelope and connected into the plate circuits of the two sections I05 and I06. The bridge circuit II2 comprises the re-- sistors H5 and H6 and the resistors IIS and I20. Potential is supplied to the bridge II2 by a transformer I2I connected across the power supply 41, the secondary winding of the transformer being connected across the resistors H5 and I20 and the resistors IIS and H9; the output being from the opposite diagonals via the leads I I3.

The phase discriminating circuit comprising the tube I04 will take the signal voltage via the leads I03 and provide a plate current through the resistors II! or II8 dependent upon the phase of the signal voltage. The plate current flowing through the resistor II! or II8 will by heat exchange, change the value of the resistor H5 or H6 to unbalance the heretofor balanced bridge circuit H2. The signal voltage provided by the unbalance of the bridge circuit is applied by the leads II3 across the resistor 29 to oppose the signal voltage as developed by the course setter 20. The opposing voltage thus developed which is dependent upon the time of the displacement, or degree of deviation, will tend to anticipate the swing of the ship back to its course to provide the necessary reverse rudder actionwhen required. By the addition of the rate circuit thus described, the ship will be kept on a true course as preset into the course setter regardless of the changes in course or degree of course deviation.

The resistor 29 is shown as a variable resistor so that the output voltage of the rate circuit may be varied. By changing the resistance value, different damping rates may be set into the system to compensate for a particular sailing or flight condition.

When the craft deviates a. slight degree from the preset course, the .bridge circuit I I2 is ineffectual, since the signal voltage is of short duration and does not presist long enough to heat either of the bridge elements H5 or IIIi. Where, however, the course of the craft is changed by rotation of the control knob 23 or is off course a considerable degree due to weather conditions, the rate circuit I00 will be effective to maintain the craft on the course as outlined. The rate circuit signal will also maintain the craft on the present course in conjunction with the signal voltages of leads 26, 21 and the feedback voltages appearing in leads 8| when crosswinds or quartering seas are encountered.

It will thus be seen that there is provided an automatic pilot for a mobile craft in which the several objects of this invention are achieved and which is well adapted to meet the conditions of practical use.

- 'As various embodiments of the above invention might be made, and as various changes might be made in the embodiments above set forth, it will be understood that all matter herein set forth or illustrated in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, we claim as new and desire to secure by Letters Patent:

' l. A steering system for mobile craft having a movable control surface thereon, comprising a motor adapted for operating said surface, direction responsive means for developing a signal when the craft departs from a prescribed course, course setter means having an input connected to said direction responsive means and an output for communicating a control signal to said motor, said motor responding to said control signal for displacing said surface to return said craft to said prescribed course, said course setter means being adapted for developing a course change signal at its output for operating said motor to displace said surface to change craft course, follow-up means operative during surface displacement for developing a follow-up signal for modifying operation of said motor, and means responsive to the signal of the output of said course setter means for deriving a damping signal therefrom for also controlling operation of said motor.

2. A steering system for mobile craft having a movable control surface thereon, comprising a motor adapted for operating said surface, direction responsive means for developing a signal when the craft departs from a prescribed course, course setter means having an input connected to said direction responsive means and an output for communicating a control signal to said motor, said motor responding to said control signal for displacing said surface to return said craft to said prescribed course, said course setter means being adapted for developing a course change signal at its output for operating said motor to displace said surface to change craft course, follow-up means operative during surface displacement for developing a follow-up signal for modifying operation of said motor, and means comprising a time delay device connected to the output of said course setter for deriving a further signal therefrom for further controlling operation of said motor.

3. A steering system for mobile craft having a movable control surface thereon, comprising a motor adapted for operating said surface, direction responsive means for developing a signal when the craft departs from a prescribed course, course setter means having an input connected to said direction responsive means and an output for communicating a control signal to said motor, said motor responding to said control signal for displacing said surface to return said craft to said prescribed course, said course setter means being adapted for developing a course change signal at its output for operating said motor to displace said surface to change craft course, manually operable means for operating said course setter means to develop said course change signal, follow-up means operative during surface displacement for developing a follow-up signal for modifying operation of said motor, and time delay means connected to the output of said course setter for deriving a further signal therefrom for further controlling operation of said motor.

4. A steering system for mobile craft having a movable control surface thereon, comprising a motor adapted for operating said surface, direction responsive means for developing a signal when the craft departs from a prescribed course, course setter means comprising a potentiometer having an input connected to said direction responsive means and an output for communicating a control signal to said motor, said motor responding to said control signal for displacing said surface to return said craft to said prescribed course, said potentiometer being adapted for developing a course change signal at its output for operating said motor to displace said surface to change craft course, manually operable means for operating said potentiometer to develop said course change signal, follow-up means comprising a second potentiometer operative during; surface displacement for developing a followup signal for modifying operation of said motor, and means connected to the output of said course setter means for deriving a further signal therefrom for further controlling operation of said motor.

5. A steering system for mobile craft having a movable control surface thereon, comprising a continuously operated motor adapted for operating said surface, means comprising a pair of solenoids adapted for selective energization determining the direction of displacement of said surface by said motor, a discriminator circuit for energizing one or the other of said solenoids depending upon the phase of an input signal applied thereto, direction responsive means for developing a signal when the craft departs from a prescribed course, course setter means having an input connected to said direction responsive means and having an output connected to the input of said discriminator circuit for operating said circuit in accordance With the signal of said direction responsive means whereby the surface is displaced to return the craft to said prescribed course, said couxse setter means being adapted for developing a course change signal at its output for displacing the surface to change craft course, follow-up means operative during surface displacement for developing a follow-up signal for modifying operation of said surface, and means connected to the output of said course setter means for deriving a further signal therefrom for further controlling operation of said surface.

6. steering system for mobile craft having a movable control surface thereon, comprising a continuously operated motor adapted for operating said surface, means comprising a pair of solenoids adapted for selective energization determining the direction of displacement of said surface by said motor, a discriminator circuit for energizing one or the other of said solenoids depending upon the phase of an input signal applied thereto, direction responsive means for developing a signal when the craft departs from a prescribed course, course setter means comprising a potentiometer having an input connected to said direction responsive means and having an output connected to the input of said discriminator circuit for operating said circuit in ac cordance with the signal of said direction responsive means whereby the surface is displaced to return the craft to said prescribed course, said potentiometer being adapted for developing a course change signal at its output for displacing the surface to change craft course, manually operable means for operating said potentiometer to develop said course change signal, follow-up means comprising a second potentiometer operative during surface displacement for developing a follow-up signal for modifying operation of said surface, and a damping circuit connected with the output of said course setter means for deriving a :further signal to provide additional control of said surface,

'7. A steering system for mobile craft having a movable control surface thereon, comprising a continuously operated motor adapted for operating said surface, means comprising pair of solenoids adapted for selective ene' ration determining the direction of displacem t of said surface by said motor, a discriminator circuit for energizing one or the other of said solenoid-s depending, upon the phase of an input signal applied thereto, direction responsive means for developing a signal when the craft departs from a prescribed course, course setter means comprising a potentiometer having an input connected to said direction responsive means and having an output connected to the input of said discriminator circuit for operating said circuit in accordance with the signal of aid direction sponsive means'ivhereby the surface displaced to return the craft to said prescribed course, said potentiometer bein adapted for developing a course change signal at its output for displacing the surface'to chan e craft course, manually operable means for operating said potentiometer to develop sa course change signal, follow-up means COl'llDilSlllQ a second potentiometer operative during surface displacement for developing a follow-up si nal for modifying operation of said surface, and means connected to the output of said course setter means for deriving a further signal thei in for further controlling operation of the surface.

8. A steering system for mobile craft having a movable control surface thereon, compris a motor adapted for operating surface, attitude change responsive means for developing afirst signal when the craft departs from a prescribed position, asecond signal developing device having a fixed part and a dispiaceable part, said device having an input connected to said attitude change responsive means and an output at which a control signal is developed corresponding to said first si; a1, a first electronic device having an input connects-:1 with the output of said signal developing device for receiving said control signal and an output connected for operating said motor, manually operable means for moving the displaceable part of said second signal developing device for producing a second control signal. at its output to modify motor operation, and a second electronic device for developing a damping signal for also controlling operation of said motor, said second electronic device having an input connected to receive at least one of said control signals and an output connected with the input of said first electronic device.

9. A steering system for mobile craft having a movable control surface thereon, comprising a motor adapted for operating said surface, attitude change responsive means for developing a first control signal when the craft departs from a prescribed position, an electronic device having an input connected to receive said signal and an output connected for operating said motor in accordance with said signal, a position change device for developing a second control signal for operating said motor and having an output connected to the input of said electronic device, and an electrical network for developing a damping signal for also controlling operation of said motor, said network having an input connected to receive at least one of said control signals and an output connected with the input of said electronic device.

ALAN M. MAcCALLUM.

CHARLES RUSSELL.

References Cited in the file of this patent UNITED STATES PATENTS Number 

